ACL Bearings Guide: Race Series vs Standard, HX Clearances & Tri-Metal Tech

ACL Bearings Guide: Race Series vs Standard, HX Clearances & Tri-Metal Tech

When it comes to engine reliability, the rotating assembly is only as strong as the thin film of oil separating your crankshaft from the engine block. If a bearing fails, the result is catastrophic metal on metal contact, usually ending with a rod through the block or a destroyed crankshaft.

Manufactured in Australia, ACL (Automotive Components Limited) is the global gold standard for performance engine bearings. Whether you are refreshing a daily driver or speccing a 1,000hp track weapon, understanding the metallurgy, clearances, and placement of your engine bearings is critical to a successful build.

Looking to protect your bottom end? Check out our complete ACL Bearings collection here!

ACL Race Series vs. Standard Bearings

ACL offers two distinct tiers of engine bearings. While standard replacement bearings are perfect for factory rebuilds, the ACL Race Series is engineered specifically for the extreme RPMs, aggressive ignition timing, and massive cylinder pressures of modern motorsport.

Feature ACL Standard Bearings ACL Race Series Bearings
Material OEM-spec Bi-Metal or Tri-Metal Hardened Tri-Metal (Copper-Lead Base)
Load Capacity Factory OEM limits Extreme loads & rapid RPM spikes
Clearance Options Standard factory replacement Available in standard ("H") or extra clearance ("HX")
Bearing Design Standard oiling grooves Enlarged chamfers & 3/4 grooving for maximum oil flow
Target Application Daily drivers, stock rebuilds High-boost turbo builds, track, drag, and drift cars


The Tri-Metal Construction (Why ACL Race Bearings Survive)

ACL Race Series bearings utilize an advanced Tri-Metal construction designed to protect your crankshaft.

  1. Steel Backing: Provides the rigid structural foundation.
  2. Copper-Lead Center: Delivers immense load-carrying capacity to withstand violent combustion forces.
  3. Lead-Tin-Copper Overlay: A microscopically thin, softer top layer. This provides "embeddability" if a microscopic particle of debris enters the oil feed, this soft layer absorbs it, pressing it into the bearing face rather than allowing it to gouge the expensive crankshaft journal.

Main Bearings vs. Conrod (Big End) Bearings

Your engine requires two entirely different sets of bearings to support the rotating assembly:

  • Main Bearings (The Anchor): These bearings are seated directly into the engine block and support the main journals of the crankshaft. They absorb the downward rotational force of combustion, ensuring the crankshaft stays perfectly aligned and spins smoothly without deflecting or vibrating.
  • Conrod Bearings / Big End Bearings (The Pivot): Seated inside the "big end" of the connecting rods, these bearings wrap around the rod journals of the crankshaft. They endure the most violent stress in the engine, translating the brutal up-and-down reciprocating force of the pistons into rotational movement.

Dialing in Clearances: H vs. HX Race Bearings

Oil clearance is the microscopic gap between the bearing face and the crankshaft journal where the oil film lives. Getting this wrong will instantly spin a bearing. ACL Race Series bearings are offered in specific sizes to help builders tune their oil pressure:

  • "H" Bearings (Standard Race): These match factory clearance specifications but feature the hardened Race Series Tri-Metal construction. Ideal for fast-road cars running standard-weight synthetic oils (e.g. 5w30 or 5w40 oil).
  • "HX" Bearings (Extra Clearance): The "X" designates an extra 0.001" (0.025mm) of oil clearance. Engine builders use HX bearings for high-horsepower track cars that run thicker racing oils (e.g., 10w60) or to compensate for crankshaft flex at extremely high RPMs where standard clearances would cause bearing binding.

Oversized Bearings: Repairing a Damaged Crank

If your engine has previously spun a bearing or the crankshaft is heavily scored, the machine shop must grind the crankshaft journals perfectly smooth again. Because grinding removes metal, the journals are now physically smaller (undersized).

To fill this new gap and restore perfect oil clearances, you must install an oversized bearing shell.

  • A +0.25mm (or +0.010") bearing is physically thicker, designed to fit a crankshaft journal that has been machined $0.25\text{mm}$ undersize.
  • Always consult with your machine shop after they have polished or ground your crankshaft to ensure you order the exact bearing thickness required for your block.

ACL Bearings provide the precision and metallurgical strength required to keep your rotating assembly alive under extreme stress. Whether you are dropping in a set of standard replacements to cure rod knock on a daily driver, or mixing H and HX shells to perfectly dial in the oil clearances on a 1,000hp drift car, ACL is the ultimate insurance policy for your engine block.